Deluge

Deluge is a full-featured BitTorrent client for Linux, Unix and Windows. It uses libtorrent in it's backend and PyGTK for it's user interface.
Deluge features a rich plugin collection; in fact, most of Deluge's functionality is available in the form of plugins.
Deluge was created with the intention of being lightweight and unobtrusive. It is our belief that downloading shouldn't be the primary task on your computer and therefore shouldn't monopolize system resources.